Load reduction in a visual rendering system

ABSTRACT

In one implementation, an electronic visual-rendering device includes an eye-tracking sensor and at least a first component. The eye-tracking sensor is configured to detect an eye-close event and, in response, output an eye-close-event message. The first component is configured to operate in at least a normal-power mode and a first low-power mode. The first components is configured to transition from operating in the normal-power mode to operating in the first low-power mode in response to the eye-tracking sensor&#39;s output of the eye-close-event message.

BACKGROUND

Some types of visually rendered media, such as immersive videos, virtualreality (VR) programs, and augmented reality (AR) programs, aretypically presented to a viewing user via a head-mounted display (HMD).Head-mounted displays include helmet-mounted displays (e.g., Jedeye, aregistered trademark of Elbit Systems, Ltd., of Haifa, Israel), headsetgoggle displays (e.g., Oculus Rift, a registered trademark of Oculus VR,LLC of Menlo Park Calif.), smart glasses, also known as opticalhead-mounted displays (e.g., Glass, a registered trademark of Google LLCof Mountain View, Calif.), and mobile-device-supporting head mounts(e.g., Google Cardboard, a registered trademark of Google LLC) thatinclude a smartphone. A head-mounted display may be a wirelessbattery-powered device or a wired wire-powered device.

A typical head-mounted VR device comprises a computer system andrequires consistently intensive computation by the computer system. Thecomputer system generates dynamic images that may be in high definitionand refreshed at a high frame rate (e.g., 120 frames per second (fps)).The dynamic images may be completely internally generated or mayintegrate generated images with image input from, for example, adevice-mounted camera, or other source. The computer system may processinputs from one or more sensors that provide information about theposition, orientation, and movement of the visual-rendering device tocorrespondingly modify the rendered image. The position, orientation,and movement of the rendered visual image is modified to correspond, inreal time, to the position, orientation, and movement of thevisual-rendering device. Additionally, the computer system may performone or more rendered-image modifications to correct for displaydistortions (e.g., barrel distortion). Furthermore, at least some of themodifications may be different for the left and right eyes of the user.

The computer system may include one or more processing units, such ascentral processing units (CPUs) and graphics processing unit (GPUs), toperform the above-described processing operations. These computationallyintensive operations contribute significantly to heat-generation withinthe processing units and the computer system, as well as to powerconsumption by the computer system. Excessive heat may triggerthermal-mitigation operations, such as throttling the processing units,which reduces the performance of the VR device and degrades the user'sexperience. Systems and methods that reduce the computational load onthe computer system would be useful for reducing the temperature of theprocessing units and avoiding thermal-mitigation throttling of theprocessing units. In addition, for battery-powered visual-renderingdevices, such as smart glasses and mobile devices inmobile-device-supporting head mounts, the reduced load would reduce thepower consumed and, consequently, extend the time until a batteryrecharge or replacement is required.

SUMMARY

The following presents a simplified summary of one or more embodimentsto provide a basic understanding of such embodiments. This summary isnot an extensive overview of all contemplated embodiments, and is notintended to either identify key critical elements of all embodiments ordelineate the scope of all embodiments. The summary's sole purpose is topresent some concepts of one or more embodiments in a simplified form asa prelude to the more detailed description that is presented later.

In one embodiment, an electronic visual-rendering device comprises aneye-tracking sensor and a first component. The eye-tracking sensor isconfigured to detect an eye-close event and, in response, output aneye-close-event message. The first component is configured to operate inat least a normal-power mode and a first low-power mode. The firstcomponent is configured to transition from operating in the normal-powermode to operating in the first low-power mode in response to theeye-tracking sensor's output of the eye-close-event message.

In another embodiment, a method for an electronic visual-renderingdevice comprises detecting, by an eye-tracking sensor, an eye-closeevent, outputting, by the eye-tracking sensor, an eye-close-eventmessage in response to the detecting of the eye-close event, operating afirst component in a normal-power mode, and transitioning the firstcomponent from operating in the normal-power mode to operating in afirst low-power mode in response to the eye-tracking sensor outputtingthe eye-close-event message.

In yet another embodiment, a system comprises means for electronicvisual-rendering, means for detecting an eye-close event, means foroutputting an eye-close-event message in response to detecting theeye-close event, means for operating a first component in a normal-powermode, and means for transitioning the first component from operating inthe normal-power mode to operating in a first low-power mode in responseto the outputting of the eye-close-event message.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed embodiments will hereinafter be described in conjunctionwith the appended drawings, provided to illustrate and not to limit thedisclosed embodiments, wherein like designations denote like elements,and in which:

FIG. 1. is a simplified schematic diagram of a device in accordance withan embodiment of the disclosure.

FIG. 2 is a flowchart for a process for the operation of the device ofFIG. 1 in accordance with one embodiment of the disclosure.

DETAILED DESCRIPTION

Various embodiments are now described with reference to the drawings. Inthe following description, for purposes of explanation, specific detailsare set forth to provide a thorough understanding of one or moreembodiments. It may be evident, however, that such embodiment(s) may bepracticed without these specific details. Additionally, the term“component” as used herein may be one of the parts that make up asystem, may be hardware, firmware, and/or software stored on acomputer-read101le medium, and may be divided into other components.

The following description provides examples, and is not limiting of thescope, applicability, or examples set forth in the claims. Changes maybe made in the function and arrangement of elements discussed withoutdeparting from the scope of the disclosure. Various examples may omit,substitute, or add various procedures or components as appropriate. Forinstance, the methods described may be performed in an order differentfrom that described, and various steps may be added, omitted, orcombined. Also, features described with respect to some examples may becombined in other examples. Note that, for ease of reference andincreased clarity, only one instance of multiple substantially identicalelements may be individually labeled in the figures.

As used herein, the term “exemplary” means “serving as an example,instance, or illustration.” Any example described as “exemplary” is notnecessarily to be construed as preferred or advantageous over otherexamples. Likewise, the term “examples” does not require that allexamples include the discussed feature, advantage, or mode of operation.Use of the terms “in one example,” “an example,” “in one embodiment,”and/or “an embodiment” in this specification does not necessarily referto the same embodiment and/or example. Furthermore, a particular featureand/or structure can be combined with one or more other features and/orstructures. Moreover, at least a portion of the apparatus describedhereby can be configured to perform at least a portion of a methoddescribed hereby.

It should be noted that the terms “connected,” “coupled,” and anyvariant thereof, mean any connection or coupling between elements,either direct or indirect, and can encompass a presence of anintermediate element between two elements that are “connected” or“coupled” together via the intermediate element. Coupling and connectionbetween the elements can be physical, logical, or a combination thereof.Elements can be “connected” or “coupled” together, for example, by usingone or more wires, cables, printed electrical connections,electromagnetic energy, and the like. The electromagnetic energy canhave a wavelength at a radio frequency, a microwave frequency, a visibleoptical frequency, an invisible optical frequency, and the like, aspracticable. These are several non-limiting and non-exhaustive examples.

A reference using a designation such as “first,” “second,” and so forthdoes not limit either the quantity or the order of those elements.Rather, these designations are used as a convenient method ofdistinguishing between two or more elements or instances of an element.Thus, a reference to first and second elements does not mean that onlytwo elements can be employed, or that the first element must necessarilyprecede the second element. Also, unless stated otherwise, a set ofelements can comprise one or more elements. In addition, terminology ofthe form “at least one of: A, B, or C” or “one or more of A, B, or C” or“at least one of the group consisting of A, B, and C” used in thedescription or the claims can be interpreted as “A or B or C or anycombination of these elements.” For example, this terminology caninclude A, or B, or C, or (A and B), or (A and C), or (B and C), or (Aand B and C), or 2A, or 2B, or 2C, and so on.

The terminology used herein is for the purpose of describing particularexamples only and is not intended to be limiting. As used herein, thesingular forms “a,” “an,” and “the” include the plural forms as well,unless the context clearly indicates otherwise. Further, the terms“comprises,” “comprising,” “includes,” and “including,” specify apresence of a feature, an integer, a step, a block, an operation, anelement, a component, and the like, but do not necessarily preclude apresence or an addition of another feature, integer, step, block,operation, element, component, and the like.

In some embodiments of the disclosure, a visual-rendering device uses aneye-tracking sensor to detect when a user's eyes close—in other words,when a user blinks. In response to determining that a blink has startedor is ongoing, the device reduces the power-level of one or moreprocessing units for a duration corresponding to the blink, and thenreturns the one or more processing units to a normal power level. Theseintermittent power reductions help to keep the one or more processingunits from overheating and to reduce power usage.

Although blinks have a very short, though variable, duration and occurat varying frequencies, their occurrences can provide useful powerreductions. Typical blinks last between 100-300 ms and occur 5-30 timesa minute. Both the duration and the frequency vary among users and overtime for the same user. In addition, users can exhibit durations andfrequencies outside the typical ranges. On average, one can expect auser's eyes to be closed for about 4 seconds out of every minute,providing a commensurate reduction in power—even considering theadditional processing needed to detect blinking and perform therequisite processing to reduce and increase power levels.

A visual rendering device may have multiple components that may bebeneficially operated at reduced power for the duration of a user'sblinks. Such components include, for example, central processing units,graphics processing units, hardware accelerators, display controllers,memories, and displays. For some circuit, reduced-power operation maycomprise, for example, operation at a reduced frequency, operation at areduced voltage, and/or a power collapse. For some components,reduced-power operation may comprise processing fewer image frames by,for example, skipping or dropping frames. For some components,reduced-power operation may comprise reducing the frame resolution ofprocessed image frames.

FIG. 1. is a simplified schematic diagram of a device 100 in accordancewith an embodiment of the disclosure. The device 100 is avisual-rendering device that comprises an eye-tracking sensor 101, asensor processor 102, a CPU 103, a GPU 104, a hardware (HW) engine 105,a display controller 106, external sensors 107, a dynamic RAM (DRAM)circuit 108, and system clock and bus controller 109. As describedbelow, the device 100 may render visual images as part of generating VR,AR, or similar immersive video for a user.

The external sensors 107, which may include accelerometers, gyroscopes,and geomagnetic sensors, provide sensor data to the sensor processor 102via path 107 a. The sensor processor 102 uses the data from the externalsensors 107 to calculate position and/or orientation information for thedevice 100, such as spatial location (x, y, z), pitch, yaw, and roll.The sensor processor 102 provides the position/orientation informationto the CPU 103, which uses that information to generate and provide tothe GPU 104 corresponding shape information that corresponds to thereceived position/orientation information and which may represent theoutlines of one or more shapes to be rendered.

The GPU 104 uses the shape information to add texture to the shapeoutlines and generate visual-rendering information for the left andright eyes. Note that the left-eye and right-eye images should beslightly different for an immersive video to replicate the parallaxeffect of viewing using two eyes located a distance apart, whichprovides appropriate depth cues. The visual-rendering information isprovided to the HW engine 105, which performs lens correction for thevisual-rendering information by suitable modification of thevisual-rendering information. The lens correction may be different forthe left and right images. The corrected visual-rendering information isthen provided to the display controller, which uses it to generatecorresponding left and right images on the display (not shown) for theuser to view.

In one implementation, data transmission between processing componentsof the device 100 may be accomplished by writing to and reading from theDRAM 108. This is illustrated by the connections to the DRAM 108 of thesensor processor 102, the CPU 103, the GPU 104, the HW engine 105, andthe display controller 106, shown as respective paths 102 a, 103 a, 104a, 105 a, and 106 a. Specifically, a data-providing component writes itsoutput to the DRAM 108 and that output is then read from the DRAM 108 bya corresponding data-receiving component. For example, the CPU 103 readsposition/orientation information, which was written by the sensorprocessor 102, from the DRAM 108 and subsequently writes correspondingshape information to the DRAM 108, which will be subsequently read bythe GPU 104.

The eye-tracking sensor 101 is a sensor that determines whether theuser's eyes are closed or closing—in other words, whether an eye-closeevent has occurred. The eye-tracking sensor 101 may monitor both leftand right eyes to determine whether both are closed/closing or it maymonitor only one eye on the assumption that both eyes blinksimultaneously. The eye-tracking sensor 101 may use any suitable sensorto determine whether an eye-close event has occurred. For example, theeye-tracking sensor 101 may use a light sensor, a near-light sensor, ora camera to determine whether the pupil, lens, iris, and/or any otherpart of the eye is visible. The eye-tracking sensor 101 may use asimilar sensor to determine the eye-coverage state of the correspondingeyelid. The eye-tracking sensor 101 may use a motion sensor to detectmuscle twitches and/or eyelid movement indicating a closing eyelid. Theeye-tracking sensor 101 may use an electronic and/or magnetic sensor(e.g., an electromyographic sensor) detect muscle activity actuatingeyelid closure or the corresponding neurological activity triggering theeyelid closure.

Upon a positive determination of eye closure by the eye-tracking sensor101, the eye-tracking sensor 101 outputs an eye-close-event message viapath 101 a. The eye-close-event message may be broadcast to the sensorprocessor 102, the CPU 103, the GPU 104, the HW engine 105, the displaycontroller 106, and the system clock and bus controller 109. The messagemay also other provided to other components (not shown) of the device100. The message may be in any format suitable for the communication busor fabric (not shown) of the device 100. In some implementations themessage may be a broadcast interrupt. In some implementations, themessage may be a corresponding signal ticking high or low or a signalpulse.

In response to receiving the eye-close-event message, the receivingcomponent may enter a low-power mode. A low-power mode for any of thecomponents may include applying one or more of the followingpower-reduction schemes to the entire component or part of thecomponent. A component may reduce its supply voltage and/or operatingclock frequency (e.g., using dynamic clock and voltage scaling (DCVS)).A component may use clock gating, which disables the clock to selectedcircuitry. A component may use power gating, which interrupts thepower-to-ground path, to reduce leakage currents to near zero. Acomponent that uses a cache may reduce its cache size. A component mayreduce the data width or other data transfer rate parameter of itsinterface. A component may reduce its memory bandwidth. A componentcomprising multiple pipelines operating in parallel may reduce thenumber of active pipelines. A component may queue events in a buffer todelay their execution or processing. A component may vary any othersuitable parameter to reduce power usage.

Particular components may employ additional types of processing powerreduction schemes. Image-frame-processing components such as the CPU103, the GPU 104, the HW engine 105, and the display controller 106 mayreduce the processing power by, for example, dropping or skippingframes. The frame refresh rate may be reduced from, for example, 120 fpsto, for example, 90, 60, or 30 fps. The image-frame-processingcomponents may reduce the image resolution and/or color palette of theprocessed frames. The system clock and bus controller 109 may reduce thesystem clock frequency and/or voltage for the device 100 in general andthe DRAM 108 in particular, e.g., via path 109 a. The GPU 104 may alsoskip normal rendering operations such as layers blending. The sensorprocessor 102 may reduce its refresh rate for providing updated positionand/or orientation information. One or more of the sensors 107 may entera low-power mode or shut down.

Note that although the display itself (not shown) may be dimmed orturned off in response to the eye-close-event message, such diming ordarkening of the screen may be visible to the user through closedeyelids, which may be disturbing and/or annoying. Consequently, thedisplay may remain on, but rendering at a lower refresh rate and a lowerresolution, in response to receiving an eye-close-event message.

Note that in some embodiments, the eye-tracking sensor 101 may controlsignal 101 a to be high when the tracked eye is closed and to be lowwhen the tracked eye is open, or vice-versa. Using the signal 101 a, acomponent receiving the signal 101 a may then set its power levelaccordingly in a manner suitable for the component.

Note that any particular component may have a plurality of low-powermodes and the particular low-power mode entered in response to receivingthe eye-close-event message may depend on any number of relevantparameters such as the instant thermal characteristics of the componentand/or the device 100, instant work load of the component and/or othercomponents of the device 100, and a battery power level of a battery(not shown) of the device 100.

The low-power mode may be in effect for a preset duration, such as 100ms. A low-power-mode duration may be provided by the eye-tracking sensor101 together with the eye-close-event message. The providedlow-power-mode duration may be updated intermittently by determiningwhen a corresponding eye-open event occurs, calculating the timedifference between the eye-close event and the eye-open event. Thelow-power-mode duration is then set to be less than the calculateddifference so that the visual rendering device will return to operatingat normal power by the time the eye is predicted to be open again. Notethat an eye-open event may be determined in any of the ways describedabove for determining an eye-close event or in any other suitable way.In other words, the eye-tracking sensor 101 may determine, depending onthe particular implementation, that the eye is affirmatively open, theeye is not closed, or that a closed eyelid is opening or about to open.

In some alternative implementations, the eye-tracking sensor 101broadcasts, via path 101 a, an eye-open-event message that is used towake up components of the device 100 from a low-power operation to anormal-power operation. Since the eye-tracking sensor 101 may detect aneye starting to open before it is fully open, the components of thedevice 100 may be back to normal-power operation by the time the eye isfully open so that the user does not see the low-power-operation visualrendering.

If the device 100 provides audio content in conjunction with the visualrendering, then the audio processing (not shown) may continue to operateat normal power—and, consequently, normal resolution, clarity, andvolume—while the above-described components of the device 100 areoperating at low power in response to the eye-close-event message. Thisis done since the user's audio experience is not affected by blinkingand should continue unmodified by blinking.

FIG. 2 is a flowchart for a process 200 for the operation of the device100 of FIG. 1 in accordance with one embodiment of the disclosure.Process 200 starts with operating a set of components of the device 100at normal power (step 201). If the eye-tracking sensor 101 determinesthat an eye-close event happened (step 202) then the eye-tracking sensor101 broadcasts an eye-close-event message to the set of components ofthe device 100 (step 203), otherwise the set of components continues tooperate at normal power (step 201) and periodically monitoring the eyefor eye closure (step 202).

In response to receiving the eye-close-event message (step 203), thecomponents of the set of components of the device 100 transition tooperating at reduced power (step 204). If a return-to-normal conditionoccurs (step 205)—such as the expiration of a duration timer or thereceipt of an eye-open-event message—then the components of the set ofcomponents return to operating at normal power (step 201), otherwise thecomponents continue to operate at reduced power (step 204) and monitorfor the occurrence of a return-to-normal condition (step 205).

As a result of running the above-described process, utilizing theabove-described system, the system can reduce its operating power andreduce the likelihood that components of the system will reach thermalthreshold temperatures that will require thermal mitigation. This, inturn, will enhance the user's experience. In addition, the reduced powerusage may increase the battery lifetime for a battery-powered system.

Note that in some embodiments, if sufficient time has passed after aeye-close-event and no eye-open-event has occurred, then the device 100may determine that the user has dozed off and, as a result, furtherreduce the power level of the components of the set of components. Thedevice 100 may, in that case, also reduce the power of othercomponents—for example, by dimming or powering down the display, ortransitioning audio components into a low-power mode.

Although embodiments of the disclosure have been described where thevisual-rendering device is part of a head-mounted display, the inventionis not limited to head-mounted displays. In some alternativeembodiments, the visual-rendering device is a mobile device that may behandheld or supported by a support mechanism or other visual-displaydevice. Such devices may also similarly benefit from the above-describedload reductions.

Those of skill in the art will appreciate that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Further, those of skill in the art will appreciate that the variousillustrative logical blocks, modules, circuits, and algorithm stepsdescribed in connection with the embodiments disclosed herein may beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, circuits,and steps have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware orsoftware depends upon the particular application and design constraintsimposed on the overall system. Skilled artisans may implement thedescribed functionality in varying ways for each particular application,but such implementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

The methods, sequences and/or algorithms described in connection withthe embodiments disclosed herein may be embodied directly in hardware,in a software module executed by a processor, or in a combination of thetwo. A software module may reside in RAM memory, flash memory, ROMmemory, EPROM memory, EEPROM memory, registers, hard disk, a removabledisk, a CD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor.

Accordingly, an embodiment of the invention can include a computerreadable media embodying a method for operating an adaptive clockdistribution system. Accordingly, the invention is not limited toillustrated examples and any means for performing the functionalitydescribed herein are included in embodiments of the invention.

While the foregoing disclosure shows illustrative embodiments of theinvention, it should be noted that various changes and modificationscould be made herein without departing from the scope of the inventionas defined by the appended claims. The functions, steps and/or actionsof the method claims in accordance with the embodiments of the inventiondescribed herein need not be performed in any particular order.Furthermore, although elements of the invention may be described orclaimed in the singular, the plural is contemplated unless limitation tothe singular is explicitly stated.

1. An electronic visual-rendering device comprising: an eye-trackingsensor configured to detect an eye-close event and, in response, outputan eye-close-event message; a first component configured to operate inat least a normal-power mode and a first low-power mode, wherein: thefirst component is configured to transition from operating in thenormal-power mode to operating in the first low-power mode in responseto the eye-tracking sensor's output of the eye-close-event message. 2.The device of claim 1, wherein the component is configured to return tooperating in the normal-power mode.
 3. The device of claim 2, whereinthe first component returns to operating in the normal-power mode aftera predetermined time period.
 4. The device of claim 3, wherein: theeye-tracking sensor is configured to detect an eye-open event and, inresponse, output an eye-open-event message; the predetermined timeperiod is variable and is based on the time difference between aprevious eye-open event and a previous eye-close event.
 5. The device ofclaim 2, wherein: the eye-tracking sensor is configured to detect aneye-open event and, in response, output an eye-open-event message; andthe first component returns to operating in the normal-power mode inresponse to the eye-tracking sensor's output of the eye-close-eventmessage.
 6. The device of claim 1, wherein: the device is a head-mounteddisplay further comprising: orientation sensors configured to outputsensor data; and a sensor processor configured to: receive the sensordata; calculate corresponding orientation information based on thereceived sensor data; output the corresponding orientation information;operate in a normal-power mode; receive the eye-close-event message; andtransition to operating in a low-power mode in response to receiving theeye-close-event message.
 7. The device of claim 1, wherein the firstcomponent is any one of a central processing unit (CPU), a graphicsprocessing unit (GPU), a hardware engine, and a display controller. 8.The device of claim 1, wherein: the device further comprises one or moreadditional components; each of the one or more additional components isconfigured to operate in at least a normal-power mode and a firstlow-power mode; each of the one or more additional components isconfigured to transition from operating in the normal-power mode tooperating in the first low-power mode in response to the eye-trackingsensor's output of the eye-close-event message.
 9. The device of claim1, further comprising a system-clock controller configured to lower asystem-clock frequency in response to the output of the eye-close-eventmessage.
 10. The device of claim 9, further comprising a memoryconfigured to operate at the system-clock frequency set by thesystem-clock controller.
 11. A method for an electronic visual-renderingdevice, the method comprising: detecting, by an eye-tracking sensor, aneye-close event; outputting, by the eye-tracking sensor, aneye-close-event message in response to the detecting of the eye-closeevent; operating a first component in a normal-power mode; andtransitioning the first component from operating in the normal-powermode to operating in a first low-power mode in response to theeye-tracking sensor outputting the eye-close-event message.
 12. Themethod of claim 11, further comprising returning to operating the firstcomponent in the normal-power mode.
 13. The method of claim 12, whereinthe first component returns to operating in the normal-power mode aftera predetermined time period.
 14. The method of claim 13, furthercomprising: detecting, by the eye-tracking sensor, an eye-open event;and output, by the eye-tracking sensor, an eye-open-event message inresponse to the detecting of the eye-open event, wherein thepredetermined time period is variable and is based on the timedifference between a previous eye-open event and a previous eye-closeevent.
 15. The method of claim 12, further comprising: detecting, by theeye-tracking sensor, an eye-open event; outputting an eye-open-eventmessage in response to the detecting of the eye-open event; andreturning to operating the first component in the normal-power mode inresponse to the eye-tracking sensor outputting the eye-close-eventmessage.
 16. The method of claim 11, wherein the device is ahead-mounted display further comprising orientation sensors configuredto output sensor data and a sensor processor, the method furthercomprising: receiving, by the sensor processor, the sensor data;calculating, by the sensor processor, corresponding orientationinformation based on the received sensor data; outputting, by the sensorprocessor, the corresponding orientation information; operating thesensor processor in a normal-power mode; receiving, by the sensorprocessor, the eye-close-event message; and transitioning the sensorprocessor to operating in a low-power mode in response to receiving theeye-close-event message.
 17. The method of claim 11, wherein the firstcomponent is any one of a central processing unit (CPU), a graphicsprocessing unit (GPU), a hardware engine, and a display controller. 18.The method of claim 11, wherein the device further comprises one or moreadditional components, the method further comprising: operating each ofthe one or more additional components in a normal-power mode;transitioning each of the one or more additional components fromoperating in the normal-power mode to operating in a first low-powermode in response to the eye-tracking sensor outputting theeye-close-event message.
 19. The method of claim 11, further comprisinglowering, by a system-clock controller, a system-clock frequency inresponse to the output of the eye-close-event message.
 20. The method ofclaim 19, further comprising operating a memory at the system-clockfrequency set by the system-clock controller.
 21. A system comprising:means for electronic visual-rendering; means for detecting an eye-closeevent; means for outputting an eye-close-event message in response todetecting the eye-close event; means for operating a first component ina normal-power mode; and means for transitioning the first componentfrom operating in the normal-power mode to operating in a firstlow-power mode in response to the outputting of the eye-close-eventmessage.